1) If they offered such services, they would either have a guitar tech on-site or ship your bass to a contracted luthier. Like Flatwound said, you have to ask.

2) I don't know, I'm a passive guy. I know that J-retro preamps can drop into the existing routing for Jazz basses. Maybe you want to check out the schematics at Fender.com (Mr. Gearhead) and see how both basses are routed.

3) I asked about the Hod-Rodded P-bass earlier and found out that you can't get an identical P-bass tone when you have the jazz pickup hooked up. You will need a switch that can separate the jazz pickup from the rest of the circuit. Mind you, this is with a passive HRP.